Draconic Vengeance

Kicker -- Reveal a red creature card from your hand. (You may reveal a red creature card from your hand in addition to any other costs as you cast this spell.)
Draconic Vengeance deals 3 damage to each creature. If this spell was kicked, it deals X damage plus 3 to each creature instead, where X is equal to the revealed creature's power.
The knights should have known better about it.